An urn contains 30 balls, of which 10 are red and 8 are blue. From this urn, 12 balls are randomly withdrawn. Let X denote the number of red and Y the number of blue balls that are withdrawn. Find Cov(X, Y)
(a) By defining appropriate indicator (that is, Bernoulli) random variables

(b) By conditioning (on either X or Y) to determine E[XY].

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10 Ai, Yi such tha t X = Σ X,, Y = Σ Y, 仁1 1-1